1. Field of the Invention
The present invention relates generally to power amplifier control of a transmitter, and specifically to power amplifier control of the transmitters of a dualband phone using a single power amplifier controller.
2. Description of Related Art
Mobile phones have recently gained widespread use throughout the world. Mobile phones communicate with a base station serving a predetermined area or cell. Each base station has a limited bandwidth within which to operate, depending upon the particular transmission technique utilized by the base station. This limited bandwidth is separated into a plurality of channels frequency-spaced evenly from one another, where these channels are used by the mobile phones within that base station's transmission area. Each base station may only handle a limited number of phones equal to the number of channels and time-slots on those channels provided by that base station. Therefore, the frequency spacing between channels is minimized in order to maximize the number of channels supported by the operating bandwidth of the base stations.
In order to prevent interference between signals on two adjacent channels, the power levels of the signals transmitted by the phones must be precisely controlled. As the mobile phones move around within a base station's cell, the power levels received at the base station will change. For instance, the power level received at the base station will increase as the phone moves closer to the base station if the signal continues to be transmitted at the same power level. Interference between adjacent channels will occur if the power level of a signal received at the base station from one of the phones is too large. Therefore, the system must constantly monitor and adjust the transmission power levels as the phones move within a base station's cell to avoid interference between channels. Most mobile phones typically have power levels between the range of 5 dBm to 33 dBm. Each phone includes a power amplifier controller (PAC) which controls a power amplifier for the transmitted signal. The PAC in each phone adjusts the transmitted power level to maintain a minimum interference between the signals received at the base station on all channels at a constant level. A certain amount of error correction is transmitted with each signal by the system, wherein the amount of error correction is predetermined based upon the constant interference level.
The capacity of base stations in highly populated areas can become saturated during time periods of high use. Mobile phones currently operate as single band phones, where the transmitted signal frequency is within the bandwidth of a base station operating on the same transmission method as the mobile phone. There is a need for mobile phones to operate with dual band transmissions to increase system capacity, so that the systems could choose between two transmission frequencies depending upon which bandwidth is less saturated and could achieve a better signal quality. A dualband phone requires two transmitters, one for each frequency band. Since the power levels of the signals transmitted by a mobile phone must be constantly adjusted, dualband mobile phones must also include a PAC for each transmitter. However, requiring two PACs in a dualband phone adds to the cost, complexity, and size of the dualband phone.
There is a need for a dualband system which selects between one of the two frequency bands to transmit a signal based upon the strength and quality of the transmitted signal received at a base station. Moreover, there is a need for a dualband phone having dualband power amplifier control using a single PAC.